The radioactive fluorine-labeling reaction has hitherto been often performed by a nucleophilic substitution reaction in which a compound S-L comprising a target substrate S and a leaving group L bonded to a fluorine-labeling site of the target substrate S is prepared as a labeling precursor compound, and then is allowed to react with radioactive fluoride ion X. In general, this reaction is performed by using a small amount of radioactive fluoride ion X for a large amount of the labeling precursor compound. Consequently, purification of the resultant radioactive fluorine-labeled compound is usually performed by separation from a large amount of the unreacted labeling precursor compound by use of HPLC method.
However, the HPLC method is cumbersome and takes time, thereby causing a factor of degradation of yield of the target compound in consideration of the half-life of radioactive fluorine of 110 minutes. As an alternative strategy needing no HPLC purification, International Publication No. WO 2009/127372 has proposed the following strategy: the portion L of the compound S-L is modified with a compound M to prepare a compound S-L-M as a labeling precursor compound; and the compound S-L-M is allowed to react with radioactive fluoride ion X to produce a radioactive fluorine-labeled compound S-X and a leaving group L-M so that the radioactive labeled compound S-X containing no M can be easily separated from the leaving group L-M and the unreacted labeling precursor compound S-L-M both of which contain M.